Lice and leg mites
Are you seeing the mites on her skin or on her legs?
One method of killing scaly leg mites would be applying oil or vaseline to the legs. Since you have to catch them at night, that may be one of the best methods since you can hopefully "paint" the oil on the legs while they roost at night.
If they are on the skin - lice/mites, then poultry dust is generally your best option.
As far as frontline I cannot say whether or not it is safe to use on poultry, you will have to research the active ingredients and make a determination whether or not the ingredients would/could be absorbed into the skin/eggs/meat.
If painting with vaseline or oil (which basically smothers the mites that are living in the scales) is not possible for the SLM you may want to look into products made specifically for SLM in poultry.
You may be able to find one made for poultry online through a pet/feed supply or on Amazon.